This invention relates to a process for producing ethylene polymers or ethylene copolymers at a pressure of at least 300 kg/cm.sup.2 and a temperature of at least 130.degree. C. More particularly, the invention relates to a process for continuously polymerizing or copolymerizing ethylene at this pressure and this temperature by the use of an ionic polymerization catalyst such as a Ziegler catalyst. A deactivator for the catalyst is added to the reaction mixture at the completion of the reaction.
As is well known, ethylene polymerization or copolymerization may be typically conducted at a pressure between 300 and 3000 kg/cm.sup.2, a temperature between 140.degree. C. and 320.degree. C. and in the presence of an ionic polymerization catalyst such as a Ziegler catalyst. In a typical process, the reaction effluent is successively introduced into two separators, one operating at high and one at low pressure. These separators remove the product polymers from the unreacted gases and are generally operated at respective pressures of 100 to 500 kg/cm.sup.2 and 1 to 50 kg/cm.sup.2.
This conventional process has several drawbacks. Under typical operating conditions, polymerization of ethylene (or, ethylene and another .alpha.-olefin) continues in the high pressure separator due to a small quantity of residual ionic polymerization catalyst discharged from the reactor. Unintended substances such as low molecular weight polymers and waxy matters can be produced. These substances affect the quality of the polymer formed and may cause clogging of pipes in the polymerization system. Also, local hot spots may form when polymerization continues outside the reactor, and thermal decomposition of ethylene can occur at these hot spots.
In order to avoid these drawbacks, U.S. Pat. No. 4,105,609 proposed a high pressure process for continuously producing ethylene polymers using an ionic polymerization catalyst. Near the outlet valve of the reactor of that process, an alkali metal compound or an alkaline earth metal salt of a saturated aliphatic or aromatic carboxylic acid was added to deactivate the active ionic polymerization catalyst discharged from the reactor. The reaction product of the deactivator and the catalyst remains with the polymer in the separator, and the addition of the deactivator does not prevent side reactions which occur in unreacted recycle gases, particularly in gases from the high pressure separator.